a.

1. 艱鉅的；費力的；困難的
   It must have been a very arduous task to build the pyramids.

   當時建造金字塔肯定是件萬分艱鉅的事。

2. 努力的；使勁的
   He made an arduous effort to keep up with the rest of the class.

   他努力跟上班上其他同學。

3. 陡峭的，難攀登的
   an arduous hill

   陡峭的山

adj.